Pre-heat the oven to 300°F.
Sear the Brisket: Pat the brisket very dry with paper towels and season generously with salt and pepper.
Heat a wide Dutch oven over medium-high heat and add olive oil. Sear the brisket on all sides until a deep crust forms, then remove and set aside.
Sauté the Onions: Add a little more oil if needed, then add the sliced onions and sauté until softened, about 2–3 minutes.
Build the Sauce: Stir in the paprika and tomato paste and sauté for another 30 seconds, breaking down the tomato paste into the oil.
Pour in the red wine and scrape up any browned bits with a spatula. Let the wine reduce for 2–3 minutes until thickened.
Braise: Return the brisket to the pot, fat side up and any accumulated juices.
In a bowl, whisk together the tomato sauce, beef stock, Worcestershire, brown sugar, and lemon juice and pour the mixture over and around the brisket.
Bring the mixture to a boil, then cover and transfer to a 300°F oven.
Braise for 3–3½ hours, or until the brisket is fork-tender and the sauce has thickened.
Slice & Serve: Transfer the brisket to a cutting board and rest for 10 minutes.
Slice against the grain, then nestle the slices back into the sauce. Spoon sauce over the top and serve.